The present application relates to a flat cable serving as an interconnecting cable for various components disposed inside various electronic devices.
Related art electronic devices such as a personal computer, a flat-screen television set, a printer, and a scanner often employ a flat cable serving as an interconnecting cable for various components to be disposed thereinside. A flexible printed circuit board type of the flat cable is produced by an etching method. However, such a type of the flat cable is costly, and a length thereof cannot be greater than 1,000 mm due to a manufacturing infrastructure, causing difficulty in being applied to the increasing size of the flat-screen television set.
A flexible flat cable produced by a laminating method, on the other hand, has attracted attention as a substitute for the flexible printed circuit board type of the flat cable. The flexible flat cable has good flexibility and can be used in a pivotable portion. Moreover, the production cost and the unit price of the flexible flat cable are lower than those of the flexible printed circuit board type. Accordingly, the flexible flat cable tends to be applied to a wide variety of fields.
Conventionally, the flexible flat cable is not demanded to have an electrical characteristic such as the characteristic impedance. For example, a related-art flexible flat cable is provided by sandwiching a central conductor 101 from both sides by base films 103 and laminating the base films 103 including a prescribed adhesion layer 102 applied thereto, so that both sides of the base films 103 are adhered as illustrated in FIG. 11, and the related-art flexible flat cable is supposed to satisfy specifications needed. Herein, the base film 103 is, for example, made of polyethylene terephthalate.
A flat cable of recent years, on the other hand, is demanded to increase the signal transmission speed with the development of various electronic devices including a flat-screen television set having a high definition image quality. The increase in the signal transmission speed is also technically needed for other electronic devices with the advancement of digitization. Accordingly, the importance of a signal integrity solution to the characteristic impedance, a permeation loss, an eye pattern aperture ratio, electromagnetic interference (hereafter referred to as EMI), and the like is rapidly increased for the signal transmission.
Such an increase in the signal transmission speed needs the control of the characteristic impedance. For example, an impedance control cable, in which the characteristic impedance is controlled, has been supplied to the market in recent years. The impedance control cable is expected not only to have enhanced capabilities thereof, but also to be produced at a low price.
Herein, a coaxial cable, serving as the impedance control cable, is formed as illustrated in FIG. 12. For example, the coaxial cable is formed of: a dielectric substance 202 covering a periphery of a central conductor 201; an outer conductor 203 covering a periphery of the dielectric substance 202; and a prescribed outer sheath 204 covering an outermost layer thereof in an insulating manner. The coaxial cable is considered to be a high-end model in terms of a high frequency characteristic, and is expensive. Moreover, since the coaxial cable is used by arranging and soldering a plurality of coaxial lines on a connector, a length thereof tends to vary, causing a propagation delay of a signal. However, the variation in the cable length cannot be reduced easily in manufacturing, and inspection of every product becomes necessary. Such inspection causes an increase in the manufacturing costs. Accordingly, a flat type of the impedance control cable has attracted attention in recent years as an alternative to the coaxial cable from a cost standpoint.
The flat type of the impedance control cable of a microstrip structure is illustrated in FIG. 13, and another flat type of the impedance control cable of a strip structure is illustrated in FIG. 14. In the impedance control cable of the microstrip structure, for example, a ground 303 is positioned on one surface of a transmission path formed of a conductor 301 and a dielectric substance 302 as illustrated in FIG. 13. In the impedance control cable of the strip structure, for example, grounds 403 are positioned on both respective surfaces of the transmission path formed of a conductor 401 and a dielectric substance 402 as illustrated in FIG. 14. The impedance control cables of the microstrip structure and the strip structure are already introduced in a market. Particularly, the impedance control cable of the microstrip structure is already employed in a certain flat-screen television set.
In the flat type of the impedance control cable, a noise source is contained by a shield layer made of metal to solve a problem of the electromagnetic interference described above, so that a leakage of the noise is reduced. Patent Documents 1 through 7 disclose and propose a shield member formed by adhesion of a metal foil to an outer sheath through a conductive adhesive agent as a technology relating to the flat type of the impedance control cable having the shield layer. Patent Document 8 discloses a shield cable formed by: folding a shield tape including a metal foil adhered to one surface side of a thermal flexible insulation sheet into two in such a manner that the metal foil is provided outward; and winding the two folded shield tape around an outer circumference of the cable.    Patent Document 1: Japanese Unexamined Patent Application Publication No. 2006-286318    Patent Document 2: Japanese Unexamined Patent Application Publication No. 2005-339833    Patent Document 3: Japanese Unexamined Patent Application Publication No. 2005-109160    Patent Document 4: Japanese Unexamined Patent Application Publication No. 2005-93367    Patent Document 5: Japanese Unexamined Patent Application Publication No. 2004-31141    Patent Document 6: Japanese Unexamined Patent Application Publication No. 2003-229695    Patent Document 7: Japanese Unexamined Patent Application Publication No. H10-145080    Patent Document 8: Japanese Unexamined Patent Application Publication No. S60-254583